Viologen (N,N-dialkyl-4,4'-dipyridinium) has an oxidation-reduction function so as to produce viologen radical when it is subjected to formation of unpaired electron, the viologen radical being easily oxidized to return to the original compound.
Further, an elastomer comprising a viologen unit is an oxidation-reduction resin, and may be an electronic conductor for oxidation-reduction reaction. Because viologen is reduced by light under a predetermined condition, an elastomer comprising a viologen unit may be used as a light energy conversion film. Because viologen cation radical produced by reducing viologen assumes a blue color or a purple color, an elastomer comprising a viologen unit exhibits photochromism and electrochromism, thus it can be used as a light quantity material, a picture recording blank material, a character display, and so forth.
Synthesis of a polymer comprising a viologen unit, which can be formed into a film form, through polycondensation reaction between diamine comprising a viologen unit and acid chloride of carboxylic acid has been reported (Journal of Polymer Science, Polymer Chemistry Edition, Vol. 13, pp. 1-16, 1975). The film formed with the above-mentioned polymer, however, was too glassy and fragile to be used as the above-mentioned material for practical use.
Further, a polymer comprising a viologen unit synthesized through cationic-polymerization of tetrahydrofuran by using mono-functional Lewis acid as an initiator has been also reported (The Society of Polymer Science of Japan, Polymer Preprints, Vol. 31, p. 330, 1982). In the case of this polymer, only one viologen unit is present in one polymer chain, and this polymer had no practical utility from the viewpoint of mechanical strength and was insufficient in exhibiting the above-mentioned functional property which is peculiar to viologen. Further, the above-mentioned report teaches another polymer comprising a viologen unit which is synthesized such that both the terminal hydroxy groups of the polyether having hydroxy groups at the terminals thereof are tosylated and then subjected to reaction with 4,4'-dipyridyl. This polymer, however, is only a dimer or trimer, and it cannot be formed into film or the like.
As described above, various syntheses of polymers comprising a viologen unit have been attempted, but it is clear from the foregoing that no polymer which can be utilized as an elastomer has yet been developed.